(1) Field of the Invention
The present invention relates to the field of aircraft flight controls. It relates to a rudder bar that is rotating for controlling yaw movements of an aircraft, and in particular of a rotary wing aircraft, and that is adjustable in position.
(2) Description of Related Art
An aircraft possesses flight controls enabling turning movements of the aircraft to be controlled about three reference axes: the roll, pitching, and yaw axes.
Movements about the roll and pitching axes are conventionally controlled by means of the pilot of the aircraft using a hand-held stick. Movements about the yaw axis are controlled by means of a rudder bar actuated by the pilot's two feet.
For an airplane, these movements are obtained by movable control surfaces situated on the wings and on the horizontal stabilizers of the airplane. For yaw movements, the rudder bar generally controls movement of a rudder located on a generally vertical fin.
Historically, a rudder bar has often been constituted in an airplane by a bar or a plank that can be turned about a vertical axis situated in the middle of the bar. The pilot then positions each foot on a respective end of the bar in order to control yaw movements of the airplane by means of two cables connecting respective ends of the bar to the rudder. Such a rudder bar together with the rudder and the cables thus constitutes a closed system.
Movements of the rudder bar are controlled by movements of the pilot's feet and legs. An action on one end of the bar of the rudder bar is then accompanied by an opposing reaction on the other end of the bar firstly because of the bar itself, and secondly via the cables that move the rudder.
In order to improve the comfort in use of a rudder bar, and in particular in order to match it to the movements made possible by the joints in the pilot's legs and feet, pedals were added to the ends of the bar. Furthermore, such pedals may be hinge-mounted relative to the bar, with respective servo-control links connecting each pedal to the bar and guaranteeing that the pedals remain parallel to each other.
Subsequently, rudder bars have been developed to use two independent pedals, each of which is provided with respective horizontal and transverse turning axes. Such a rudder bar then co-operates with the rudder and with the cables controlling movements of the rudder to form an open system. An action on a pedal is then accompanied by an opposing reaction on the other pedal that is developed solely by means of the cables.
In contrast, for a rotary wing aircraft, movement of the aircraft about the yaw axis is generally not obtained by moving a rudder, but rather by varying the collective pitch of the blades of a yaw anti-torque rotor.
Nevertheless, an architecture identical to that of an airplane was used for installing yaw flight control on rotary wing aircraft, as initially designed by airplane designers. The rudder bar of a rotary wing aircraft thus generally comprises two pedals having respective turning axes about the transverse direction of the aircraft. The pedals are connected to a mechanical transmission linkage in order to transmit collective pitch variation orders for the anti-torque rotor from the rudder bar to the anti-torque rotor.
Nevertheless, acting on a pedal of such a rudder bar does not lead to any reaction on the other pedal being generated by the anti-torque rotor. As a result, mechanical coupling has been added in order to connect together the two pedals of the pedal set. Furthermore, mechanical coupling must also be put into place between the pilot's rudder bar and the rudder bar for the copilot of the aircraft. By way of example, such mechanical coupling may be provided by means of tube and links.
Furthermore, an additional braking function has been added to the rudder bars of certain aircrafts. The braking function makes it possible to act on the pedals to obtain differential braking on one or more wheels of the aircraft landing gear. This braking can be made available on rotary wing aircraft having wheeled landing gear. This braking function serves firstly to slow down and to stop the aircraft on the ground, and secondly to steer it on the ground.
Installing a rudder bar on a rotary wing aircraft is often complex, since the layout of the rudder bar needs to be adapted to each aircraft as a function of the mechanical configuration of the aircraft. In particular, the architecture of the aircraft imposes constraints, such as the positions of frames and longerons, and also the space available under the floor for installing the pedal set. Furthermore, additional constraints are involved with mechanically transferring orders for varying the collective pitch of the blades of the anti-torque rotor and also for varying the positions and the adjustments of the seats for the pilot and for the copilot.
In order to simplify the description and except where specifically contrasted with the term “copilot”, the term “pilot” is used in the description below to specify equally well a pilot or indeed a copilot.
Furthermore, in order to be able to adapt to the morphology of pilots, which may be extremely varied, thereby improving the comfort and the piloting position of the pilot, a rudder bar is nowadays often adjustable at least in the longitudinal direction of the aircraft, even though the seat is itself also adjustable in the longitudinal direction.
Specifically, adapting the piloting position of a rotary wing aircraft to the length of a pilot's legs is a major problem when designing rotary wing aircraft. This adaptation is made that much more complex in that it needs to take account in particular of the mechanical coupling that is needed both between the two pedals of one rudder bar and between the rudder bars of the pilot and of the copilot.
By way of example, Document US 2008/0105790 discloses a rudder bar in which the pedals are adjustable in position in the longitudinal direction of the aircraft. That rudder bar has rails for sliding, together with a notched rail for blocking such sliding by means of a locking device. That rudder bar is for use with electrical flight controls of an aircraft and it may include a force return system. That rudder bar also enables the braking function to be used.
Furthermore, Document US 2014/0131523 describes a modular rudder bar suitable for being installed directly on the floor of an airplane. The rudder bar is for electrical flight controls and it too enables the braking function to be used. That rudder bar includes means for adjusting the longitudinal position of each pedal, and also its angle of inclination.
Also known is Document US 2014/0251066, which describes a system having at least one pedal of position that is adjustable in order to adapt to the size of a pilot. By way of example, that system may be used for controlling braking or yaw movements of an aircraft. That system may be adapted to flight controls that are electrical or indeed mechanical. The positions of the pedals in that system can be adjusted both longitudinally and in height. For such height adjustment, a portion of the system, including the longitudinal adjustment of the pedals, is inclined relative to the floor of the aircraft so that the pedals are higher when they are closer to the pilot's seat. As a result, the pedals can be too high for a short pilot when the pedals are moved longitudinally towards the pilot's seat. In contrast, when the pedals are moved longitudinally away from the seat for a tall pilot, the pedals remain close to the floor of the aircraft.
In addition, Document U.S. Pat. No. 2,478,882 describes a rudder bar that is longitudinally adjustable and that comprises two pedals, a main body, and a pedal bar. The pedal bar is connected to the main body via a slideway connection enabling the pedals of the rudder bar to be adjusted longitudinally. The main body is secured to a vertical shaft that is movable in turning and to a set of connecting rods enabling the two pedals to remain parallel to a transverse direction. The rudder bar may also incorporate a braking device activated by pressing on the pedals.
In addition, Document U.S. Pat. No. 4,484,722 describes a device for moving the pedals of a rudder bar and the pedal bar in translation relative to the main body depending on the inclination of the seat for the aircraft pilot. A screw-and-nut system with rotation of the screw being driven by inclining the seat causes the pedals of the rudder bar to move along rails.
Also known is Document U.S. Pat. No. 3,377,881, which describes a rudder bar in which the longitudinal position of the pedals is adjustable. The rudder bar has two connecting rods and two links forming a parallelogram so as to keep the pedals parallel to each other. Furthermore, each pedal is connected to a link by three arms enabling it to be adjusted longitudinally. The adjustment of the position of one pedal is independent of the adjustment of the position of the other pedal.
Finally, the technological background includes Documents US 2013/0019706, FR 2 660 028, and GB 302137.
In addition, for mechanical flight controls of a rotary wing aircraft, a mechanical transmission linkage transmits orders for varying the collective pitch of the blades of the anti-torque rotor from the rudder bar to the anti-torque rotor. The mechanical transmission linkage is generally situated under the floor of the aircraft, a mechanical connection then connecting the rudder bar to said mechanical transmission linkage. Specifically, when the position of the pedal set, or indeed of the pedals, is longitudinally adjustable, a longitudinal opening needs to be made in the floor of the aircraft in order to enable the mechanical connection between the rudder bar and the mechanical transmission linkage to be moved. Consequently, there exists a risk that foreign bodies can penetrate through the opening, which foreign bodies might block the mechanical transmission linkage between the rudder bar and the anti-torque rotor.